IMPROVING UIS GAS DRAINAGE IN UNDERGROUND COAL MINES

Transcription

1 IMPROVING UIS GAS DRAINAGE IN UNDERGROUND COAL MINES Dennis J. Black 1,2 and Naj I. Aziz 1 ABSTRACT Gas drainage is considered one of the most effective controls in preventing coal and gas outbursts. The advances in mining equipment technology over the last 20 years have led to a significant increase in coal mine production, resulting in increased coal mine gas emission during the coal extraction process. High gas emissions, if not effectively managed, may exceed the diluting capability of the mine s ventilation system, potentially exceeding the statutory limit, resulting in gas related production delays. The development of underground to inseam (UIS) gas drainage is discussed. The study is focused on a range of factors which impact gas drainage and proposes actions to improve drainage performance. INTRODUCTION Many Australian underground coal mines are progressing toward areas which require the use of gas drainage to reduce seam gas concentrations to below a prescribed Threshold Limit Value (TLV). In a number of cases, these mines will encounter areas where the gas is extremely difficult to drain from the coal, ahead of mining. Where difficult drainage areas are encountered, the mines may be faced with significant production delays while intensive drilling is carried out to reduce the gas concentrations to acceptable levels. To avoid such costly delays, mine management may choose to avoid the area completely, resulting in loss of reserves, loss of potential revenue, and ultimately reduced mine life. This project aims, through an integrated series of site based and laboratory studies, to determine the relative impact and significance of a broad range of factors which impact gas drainage in underground mines. A further aspect of this study involves the assessment of a range of actions, based on knowledge of the factors identified in the early stage of the project, which can be taken by the mine operator to improve gas drainage performance, enabling the potentially sterilised areas to be accessed and extracted. BACKGROUND This study focuses on gas drainage experience in the Bulli seam which is located in the southern Sydney Basin in New South Wales, Australia. The seam is stratigraphically the uppermost coal seam in the Permian Illawarra Coal Measures. The depth of cover, in the area of study is in the order of 450 to 500 metres with a regional dip of approximately 1.9 degrees, toward the west. The gas composition in the mining domain is variable, ranging from almost pure CH 4 in the east to almost pure CO 2 in the west. Table 1 contains details of the range of coal properties investigated, which are characteristic of the mining area investigated, known as Mine A. Table 1: Coal properties investigated in the mining area analysis Coal Property Minimum Maximum CH4 ratio (CH 4/CH 4+CO 2) Gas Content (m 3 /t) Permeability (md) Seam thickness (m) Ash content (%) Moisture content (%) Vitrinite reflectance (R v(max)) Vitrinite (%) Inertinite (%) Mineral matter Volatile matter 6.5% 5.2 m 3 /t 0.05 md 2.33 m 9.4 % 0.7 % % 45.51% 1.8% 19.7% 97.8% m 3 /t 6 md 3.19 m 14.8 % 1.3% % 71.1% 5.78% 25.25% The Bulli seam is extremely prone to the occurrence of coal and gas outbursts. During the history of mining in the Bulli seam there have been 12 reported fatalities associated with outbursts, listed in Table 2. 1 Department of Civil, Mining and Environmental Engineering, University of Wollongong, Australia 2 Pacific Mining and Gas Management (PacificMGM),

2 Table 2: Fatal outbursts in the Bulli seam (source, Harvey and Singh, 1998) COLLIERY DATE No. KILLED SIZE (tonnes) GAS STRUCTURE Metropolitan 10 June Unknown CH4 Dyke and soft fault Metropolitan 27 July CO 2 Fault with 5m throw Metropolitan 2 December CO 2 Normal fault with 0.3m throw Tahmoor 24 June CO 2 Dyke associated with strike-slip movement Thrust fault with 0.35m of mylonitic coal South Bulli 25 July CO 2 & CH 4 and very high gas pressure Intersection of 2 strike-slip structures and West Cliff 25 January CO 2 0.3m of mylonitic coal The most effective method of preventing an outburst is through the reduction of seam gas content and gas pressure, Lama (1980), Marshall, Lama and Tomlinson (1982) and Wood (1983). Over the years, many different approaches have been undertaken, by various mine operators, to reduce gas levels and pressures to manageable levels with mixed success. However, the current advanced gas drainage technology is proving the most effective, Clark et al. (1983). Prior to 1980, gas drainage was achieved through drilling relatively short holes, typically 25 to 40 metres ahead of the working face, using primarily hand-held borers to drill holes of varying diameters, ranging from 43 mm to 100 mm, without any applied suction (Hargraves, 1983). Through advances in equipment technology increased coal production was achieved, however this also resulted in increased gas emissions into the mine airways. In order to prevent these gas emissions from exceeding the diluting capability of the mine s ventilation system, regular, efficient gas drainage programs were required to reduce the gas content of the coal prior to mining, in addition to reducing the outburst risk. In 1980, West Cliff colliery commenced the first routine pre-drainage drilling and gas drainage program, ahead of mining. Since the commencement of underground-to-inseam (UIS) drilling the equipment has evolved from simple rotary drilling rigs with directional control accuracy of ±15 o for hole lengths of m (Hebblewhite et al., 1982, Hebblewhite et al., 1983 and Kelly, 1983) to technically advanced units incorporating down-hole motors, with in-hole data acquisition tools, capable of drilling distances beyond 1,600 metres with survey accuracy in the order of ±0.5 o azimuth and ±0.2 o pitch (Valley Longwall Drilling). Although aware of the relationship between gas and outburst risk, and the impact of gas drainage on reducing this risk, many operators failed to implement systems to regularly check and assess the outburst risk ahead of future workings. Following the investigation into the last fatal outburst, which occurred in the Bulli seam at West Cliff colliery on 25 January 1994, a directive was issued to all Bulli seam coal mine operators, under the authority of the Coal Mines Regulation Act 1982, prescribing threshold limit values (TLV), and other actions, to be implemented to manage risk and prevent future coal and gas outbursts. The Department of Mineral Resources, New South Wales, introduced The Outburst Mining Guideline, MDG 1004, in 1995, which led to the development and implementation of Outburst Management Plans, as part of the mine safety management system. Intensive UIS drilling programs are used to collect coal cores for gas content testing, identify structures ahead of the mine workings, as well as draining gas to below the TLV. The outburst threshold limit graph, shown in Figure 1, is typical of those introduced at each of the Bulli seam mines, and now forms an integral part of Outburst Management Plans (Figure 1), specifies maximum gas content to which the seam must be drained before approval may be given to mine the area. Given the high gas content throughout the Bulli seam, the introduction of the TLV graph has led to the development and implementation of intensive pre-drainage drilling programs aimed at reducing seam gas contents to below the applicable TLV, to avoid delays to the roadway development and longwall operations. Many of the Bulli seam mines now employ extensive gas drainage programs with greater than 100,000 metres of underground to inseam (UIS) pre-drainage boreholes being drilled annually. However, even with the application of such intensive UIS drilling, there are a number of mining areas, past, present and future, which will experience difficulty reducing the gas content to below the TLV. This poor drainage is caused by a variety of geological conditions and operational factors which adversely impact drainage performance. A number of interrelated projects are now being undertaken at the University of Wollongong to quantify the factors that impact gas drainage and to evaluate suitable drainage improvement initiatives that may be implemented by mine operators to address the poor drainage zones.

3 Outburst Threshold Limit Values /t ] FULLY REMOTE MINING OUTBURST or REMOTE MINING Total Gas Content [ m 6 4 NORMAL MINING Gas Composition [ CO 2 /(CH 4 +CO 2 ) ] Figure 1: Typical outburst Threshold Limit Value (TLV) graph PROJ ECT OUTLINE & OBJECTIVES The objective of this project is to develop an understanding of the factors which impact gas drainage and to determine suitable actions that may be implemented to successfully treat the identified difficult drainage zones, ahead of mining, enabling these zones to be accessed and extracted, without incurring any unacceptable gas drainage related production delays. The process to achieve this objective, summarised in Figure 2, involves both site-based and laboratory testing and analysis. The initial work programme focussed on determining the factors which have most impact on gas drainage, based on the collection and analysis of the following: gas flow data from UIS drill holes; coal core gas and quality data; and collect and test coal samples to determine properties and characteristics. The second phase involves the investigation, evaluation and possible trial of a range of potential drainage improvement techniques, to improve gas drainage effectiveness. MINE S ITE ANALYS IS Gas flow data has been collected from 306 UIS boreholes, covering an area which encompasses four separate longwall panels in a local mine (Mine A). The location of the boreholes and coal cores analysed during this study are shown in Figure 3. A review of the entire dataset identified that 118 holes (38.5 % of the total holes) were compromised in some way, either through blockage or flooding, overlapping with adjacent boreholes, or very short life. These holes were excluded from the dataset as the flow data was deemed to be questionable and not representative of reasonable conditions. Gas flow data from the remaining 188 boreholes form the basis of the analysis. Table 3 lists the panels and number of boreholes from each which were included in the overall borehole flow analysis.

4 COAL CORE ANALYSIS BOREHOLE GAS FLOW ANALYSIS GENERAL DATA SLOW DESORPTION (AS ) DETERMINE: Gas Content Gas Composition Sample Location Gas Emission Rate Δ Gas Composition Retained Gas Content (Q3) Petrographic Analysis QUICK TEST (AS ) DETERMINE: Gas Content Gas Composition Sample Location BOREHOLE DATA DETERMINE: Length Orientation Apparent Dip Suction Pressure GAS FLOW DATA DETERMINE: Gas Emission Rate Cumulative Gas Drained Δ Gas Composition DETERMINE: Seam Thickness Depth of Cover Gas Content Gas Composition Stress Direction & Magnitude Permeability Piezometer Data seam pressure Coal Quality Data Relevant Sorption Data Analyse gas emission from coal cores from current mining area to determine: (a). the naturally retained gas content (Q3); (b). the rate of gas emission; and (c). changes in emitted gas composition through desorption. The gas desorption results will be compared to results of petrographic analysis on the coal cores to determine relationships that may exist and impact gas drainage rate. Detailed analysis of gas drainage experience in current mining domain determine: (a). Factors and conditions that impact gas drainage performance; (b). Opportunities to improve / optimise current underground to inseam (UIS) gas drainage program; and (c). Identify areas where the ongoing use of UIS drilling alone will not achieve satisfactory drainage SORPTION TESTING SHRINKAGE TESTING ASSESS ALTERNATE GAS DRAINAGE IMPROVEMENT OPTIONS Test coal samples from a range of areas, representing different insitu conditions, and determine response to different gases. Assess results and relate to the data obtained from site-based analysis of gas drainage experience and gas desorption analysis Identify and evaluate a range of alternate drilling and stimulation options that may be employed by the mine to address areas of known difficult drainage. Compile results of all analysis and investigation undertaken, summarising the opportunities that exist for the Colliery to improve the effectiveness of the current UIS gas drainage system, identify areas where the current drainage system will likely be ineffective and make recommendation regarding alternative method that may be employed to improve gas drainage performance. Figure 2: Project flowchart Figure 3: UIS borehole and coal core locations analysed (Mine A)

5 Table 3: Borehole number and location analysed in Mine A UIS Borehole Gas Flow PANEL Analysis TOTAL Time on Suction no. % no. % no. % no. % no. % no. % Drill Stubs Recorded Total holes in drill stub No. holes <100 days % % % 0 0.0% 0 0.0% % No. holes <50 days % % % 0 0.0% 0 0.0% % Total holes included in analysis (after short life holes {<30 days}, obvious failed holes {blocked & flooded} and overlapping holes removed from dataset) % % % % 0 0.0% % Figure 4 shows the distribution of total gas production of all 188 boreholes included in the dataset. 90 West Cliff Mine - Area 5 Gas Analysis Borehole Flow Analysis - Distribution of Total Gas Production Frequency Total Gas Production (m3) Figure 4: Distribution of total gas production from UIS boreholes Table 4 lists the variables that were considered to have an impact on total gas production. Table 4: Factors initially considered to impact gas drainage Borehole length Borehole orientation to cleat (100/280) Borehole orientation to stress Borehole apparent dip Gas content (m3/t) Gas composition (%CH4) Time on suction (days) Suction pressure (kpa) - median Seam thickness Moisture content Reflectance Rv(max) Permeability (md) Ash content Intertinite component Vitrinite component Mineral component RESULTS AND DISCUSSION A detailed statistical analysis was performed on the dataset from which the correlations, shown in Table 5, were determined. Table 5 is split into the factors that are (a) considered naturally occurring and therefore not controllable, and (b) those on the right which the operator has a certain degree of control over. Using statistical analysis, virtually no correlation was found between total gas production and the following variables; (a) borehole orientation to cleat, (b) borehole orientation to stress, and (c) apparent dip, yet a review of the data distribution indicated ranges where greater gas production was achieved. Figure 5 shows the distribution of gas production data for these three variables.

6 Table 5: Statistical correlation results from complete dataset analysis Factor assessed for correlation R 2 Factor assessed for correlation R 2 Gas composition (%CH4) 42 Time on suction (days) 18 Gas content (m3/t) 32 Suction pressure (kpa) - median 10.2 Seam thickness 25 Borehole orientation to stress 6 Permeability (md) 19 Borehole length 3.9 Reflectance Rv(max) 17 Borehole orientation to cleat (100/280) 1.1 Intertinite component 17 Borehole apparent dip 0 Vitrinite component 16 Mineral component 8 Ash content 6 Note: R 2 represents the percentage variation of the variable relative to the regression model for the dataset. The higher the R 2, the better the regression model fits the data. Figure 5: Gas production data distribution relative to borehole orientation and apparent dip The dataset was refined to include only those meeting all three of the criteria listed below. Further analysis was undertaken on the refined dataset to include: Borehole orientation to cleat (100/280): 20 to 70 degrees; Borehole orientation to stress: 0 to 50 degrees; and Borehole apparent dip: 0.0 to +1.6 degrees. Table 6 shows the results of the statistical analysis on the dataset which satisfied the above listed criteria. Table 6: Correlation results for data fitting borehole orientation and apparent dip criteria Factor assessed for correlation R 2 Factor assessed for correlation R 2 Gas content (m3/t) 30.0 Time on suction (days) 32.0 Gas composition (%CH4) 29.0 Borehole length 2.0 Reflectance Rv(max) 20.9 Suction pressure (kpa) - median 1.8 Seam thickness 20.8 Borehole orientation to stress 0.0 Permeability (md) 13.7 Borehole orientation to cleat (100/280) 0.0 Mineral component 10.6 Borehole apparent dip 0.0 Intertinite component 5.9 Moisture content 5.8 Ash content 5.7 Vitrinite component 5.2 Note: R 2 represents the percentage variation of the variable relative to the regression model for the dataset. The higher the R 2, the better the regression model fits the data. As expected, there was no correlation between gas production and the three variables used to refine the dataset. The controllable variable, time on suction, maintained the strongest correlation with total gas production. Given the relatively narrow range of apparent dip (0 to +1.6 degrees) the dataset was expanded to cover an increased apparent dip range, considered to provide greater flexibility for mine site deployment. The results of the statistical analysis on the dataset satisfying the criteria, listed below, are provided in Table 7.

7 Borehole orientation to cleat (100/280) 20 to 70 degrees Borehole orientation to stress 0 to 50 degrees; and Borehole apparent dip 0 to degrees. Table 7: Correlation results for data fitting borehole orientation and apparent dip criteria Factor assessed for correlation R 2 Factor assessed for correlation R 2 Gas composition (%CH4) 33.0 Time on suction (days) 20.0 Gas content (m3/t) 30.0 Borehole length 6.7 Reflectance Rv(max) 21.0 Borehole apparent dip 3.0 Seam thickness 21.0 Suction pressure (kpa) - median 2.0 Permeability (md) 14.0 Borehole orientation to stress 1.3 Mineral component 11.0 Borehole orientation to cleat (100/280) 1.0 Intertinite component 6.0 Ash content 6.0 Moisture content 5.0 Vitrinite component 5.0 Note: R 2 represents the percentage variation of the variable relative to the regression model for the dataset. The higher the R 2, the better the regression model fits the data. The results show the controllable variable, time on suction, continues to maintain the strongest correlation with total gas production. As shown in the results of the statistical analysis above, of all the non-controllable factors considered, both gas composition and gas content have the strongest correlation with total gas production. Figure 6 shows the distribution of total gas production relative to both gas composition and gas content. Figure 6: Distribution of gas production data relative to gas composition and content Although both graphs show increasing total gas production with increasing composition and content, the gas composition appears to be the most dominant. In areas where CO 2 is the dominant gas, the total gas production is generally low, typically less than 200,000 m 3. In the areas where CH 4 is the dominant gas, far greater total gas production was achieved, particularly where the CH 4 composition was greater than 80%. It must however be recognised that although it is possible to achieve very high gas production in the high CH 4 zones, there are also a significant number of very poor producing boreholes. The dataset was refined on the basis of boreholes whose gas composition ranged between 0 and 40% CH 4. Table 8 shows the results of the statistical analysis on this dataset. It can be seen that time on suction continues to maintain the strongest correlation to total gas production of all the controllable factors considered. Suction pressure also has a far greater correlation to total gas production in the high CO 2 zones. The results also show increased correlation between a number of the non-controllable factors and total gas production, in particular permeability and moisture content. A similar analysis was conducted on a refined dataset covering all borehole data within the gas composition range of 70 to 100 % CH 4. Table 9 shows the results of the statistical analysis on this dataset. Similar to the previous analysis, time on suction continues to maintain the strongest correlation to total gas production of all the controllable variables considered. There is generally low correlation between all of the non-controllable factors and total gas production which is due to the high degree of variability in the total gas production of the boreholes in the high CH 4 zones.

8 Table 8: Correlation results for data fitting the high CO2 criteria (0 40% CH4) Factor assessed for correlation R 2 Factor assessed for correlation R 2 Permeability (md) 77.0 Time on suction (days) 54.0 Gas composition (%CH4) 43.0 Suction pressure (kpa) - median 42.0 Moisture content 36.0 Borehole apparent dip 9.0 Mineral component 26.0 Borehole length 0.0 Gas content (m3/t) 22.0 Borehole orientation to stress 0.0 Vitrinite component 21.0 Borehole orientation to cleat (100/280) 0.0 Reflectance Rv(max) 20.0 Seam thickness 16.0 Intertinite component 13.0 Ash content 5.0 Note: R 2 represents the percentage variation of the variable relative to the regression model for the dataset. The higher the R 2, the better the regression model fits the data. Table 9: Correlation results for data fitting the high CH 4 criteria (70 100% CH 4) Factor assessed for correlation R 2 Factor assessed for correlation R 2 Gas composition (%CH4) 8.0 Time on suction (days) 29.0 Reflectance Rv(max) 8.0 Borehole orientation to stress 14.0 Moisture content 6.3 Borehole orientation to cleat (100/280) 12.0 Gas content (m3/t) 4.2 Borehole apparent dip 2.0 Seam thickness 0.6 Suction pressure (kpa) - median 1.0 Permeability (md) 0.0 Borehole length 0.0 Mineral component 0.0 Vitrinite component 0.0 Intertinite component 0.0 Ash content 0.0 Note: R 2 represents the percentage variation of the variable relative to the regression model for the dataset. The higher the R 2, the better the regression model fits the data. Capability assessment was then undertaken to determine statistically the impact on total gas production which may be expected through optimising the UIS gas drainage program, based on the results of the gas data analysis. The two areas where improvement and optimisation were considered possible are: Borehole orientation; and Gas drainage system maintenance. As discussed previously, the gas production data indicates an optimum borehole trajectory exists in relation to cleat direction, stress direction and apparent dip. Statistical capability analysis determined that a % increase in average total gas production may be achieved by maintaining all UIS boreholes to within the following criteria: Borehole orientation to cleat (100/280) 20 to 70 degrees Borehole orientation to stress 0 to 50 degrees; and Borehole apparent dip 0 to +1.6 degrees. Where the range of the apparent dip is increased to cover the range 0 to 3.25 degrees the capability assessment concluded that a % increase in average total gas production may be achieved. Also, some 82 boreholes (26.8 % of the total boreholes), achieved low total gas production, less than 100,000m 3. However, the statistical analysis did not find any relationship between the factors considered and poor production. Although not analysed in this study, regular problems with UIS boreholes were reported which included; borehole blocked, borehole full of water and no suction. It is believed that through focussed system management, which includes regular assessment of borehole flow performance that holes which perform below expectation may be quickly identified and appropriate corrective action may be taken to improve drainage. Statistical capability assessment was used to assess the impact on average total gas production by addressing the boreholes producing less than 100,000 m 3. The impact was determined through eliminating the low producing holes from the dataset. The result was a % increase in average total gas production. At an estimated cost of $20,000 for each installed UIS drainage borehole, significant financial benefit and gas drainage effectiveness (m 3 /$) could be realised

9 through implementing measures to avoid failed and poor producing holes. Table 10 lists the results of this statistical capability assessment. Table 10: Results of statistical capability assessment of UIS borehole gas production dataset Capability assessment - Total Gas Production (m 3 ) No. of samples Mean Total Gas Production (m3) Average production increase (%) ALL Data ,183 Status Quo Data fitting the Orientation & Dip condition , % Data outsite the Orientation & Dip condition ,573 Data fitting the Orientation condition, Dip range increase to (0 o o ) , % Data outside the Orientation condition, Dip range increase to (0 o o ) ,163 Data greater than 100,000m 3 total gas production , % Data less than 100,000m 3 total gas production 82 48, 822 Data fitting the Orientation & Dip condition & >100Km 3 production , % Data fitting the Orientation condition, Dip range (0 o o ) and >100Km 3 total production , % CONCLUSIONS This study identified that a significant portion of the drilling effort yields little benefit to the overall gas drainage effort. Of the 306 UIS boreholes studied, 118 (38.5%) were found to be either blocked, flooded or had an effective drainage life of less than 30 days prior to being intersected by compliance drilling or roadway development. A further 82 (26.8%) achieved total gas production of less than 100,000m 3. Of the six controllable factors, listed below, which were included in the analysis, time on suction consistently recorded the highest correlation to total gas production. The other factors in the order of correlation significance include: Suction pressure Borehole orientation relative to cleat Borehole orientation relative to stress Borehole apparent dip Borehole length In high CO 2 zones, the gas production achieved was typically low, at less than 200,000 m 3. In the high CH 4 zones, there was significant variation in the total gas production, ranging from extremely poor (~0 m 3 ) through to extremely high (~900,000 m 3 ). However, there was strong correlation between total gas production and time on suction and borehole trajectory. Borehole orientation and apparent dip have a significant influence on total gas drainage. Boreholes oriented 20 to 75 degrees relative to the dominant cleat, and 0 to 50 degrees relative to the major horizontal stress and with an apparent dip in the range of 0 to +1.6 degrees were found to have an average total gas production 54 % greater than the complete dataset and 97 % greater than those holes outside this range. Also, by eliminating the poor producing holes (those achieving less than 100,000 m 3 ), implementing systems and measures to improve borehole integrity, and ongoing borehole and gas drainage system management, issues such as blockages, flooding and short lead times could be prevented. By improving the management and maintenance of the entire system, to reduce or eliminate the number of failed and poor producing boreholes, has the potential to increase the average total borehole gas production by up to 56 %. Combining both optimised borehole trajectory and improved system management it may be possible to more than double the average borehole total gas production capability. Although gas production in high CO 2 zones is impacted more by non-controllable factors than in the high CH 4 zones, however, finite improvement in gas production from UIS boreholes can be achieved by: Borehole maintenance, to avoid blockages, etc.; Optimise borehole trajectory relative to cleat, stress and apparent dip; Maximise drainage time; and Maintain high suction pressures ACKNOWLEDGEMENTS The contributions of Matthew Jurak and Kate Lennox with the collection are recognised and greatly appreciated.

10 REFERENCES Clark, D. A., Battino, S. and Lunarzewski, L. (1983) Prevention and control of outbursts by pre-drainage of seam gas at Metropolitan colliery a review. Alleviation of Coal and Gas Outbursts in Coal Mines Seminar 3. Co-ordinating Committee on Outburst Research. September Coal Mining Inspectorate and Engineering Branch (1995) Outburst Mining Guideline MDG No:1004, Department of Mineral Resources New South Wales. Harvey, C. R. and Singh, R. N. (1998) A review of fatal outburst incidents in the Bulli seam, Proceedings of the 1 st Australasian Coal Operators Conference Coal98, University of Wollongong, February 1998 pp Hebblewhite, B.K, Richmond, A.J. and Richards, J. (1982) Australian experience in longhole in-seam drilling technology for seam gas drainage, in Proceedings Seam Gas Drainage with Particular Reference to the working seam, AusIMM Illawarra Branch, May, University of Wollongong, pp Hebblewhite, B.K, Sheppard, J., Nixon, L.K. (1983) The use of gas drainage and role of structural geology in outburst prevention, Alleviation of Coal and Gas Outbursts in Coal Mines, Coordinating Committee on Outburst Research, 1983 Kelly, M. (1983) Practical in-seam drainage at Appin colliery, Alleviation of Coal and Gas Outbursts in Coal Mines, Coordinating Committee on Outburst Research, 1983 Lama, R. D, Marshall, P. and Griffiths, L. (1980) Methane drainage investigations as a method of control of outbursts at West Cliff colliery. The Occurrence, Prediction and Control of Outbursts in Coal Mines Symposium. AusIMM Southern Queensland Branch. September, Lama, R. D. (1995) Evaluation of in-seam borehole stability in coal mines, ACARP Project C3029, Australian Coal Association Research Program. Marshall, P., Lama, R. D. and Tomlinson, E. (1982) Experience on pre-drainage of gas at West Cliff Colliery, in Proceedings Seam Gas Drainage with Particular Reference to the working seam, AusIMM Illawarra Branch, May, University of Wollongong, pp Wood, J. H. and Hanes, J. (1983) Development of techniques for prevention of outbursts, Alleviation of Coal and Gas Outbursts in Coal Mines Seminar 3. Co-ordinating Committee on Outburst Research. September 1983.